Modern cranes have a plurality of degrees of freedom, particularly a plurality of movements executable for example by its extendable arm or by the components thereof. Such movements are usually commanded by an operator by means of a remote command device, typically a radio command. Such command device comprises a plurality of levers actuatable by the operator, a specific movement and the direction thereof of the crane corresponding to each of them.
The increasing versatility of hydraulic cranes, capable of executing plural movements, causes also an increasing complexity of the command devices which feature several commanding members actuatable by the operator, so that there is a consequent increase of the risk of errors and therefore of failures of the crane, or even injuries to the operator.
Particularly, overload situations of one or more of the parts of a crane, which could cause the crane to flip over or to be damaged, are prevented by automatically switching the crane to a stoppage state in order to prevent the operator to perform some harmful operations, enabling at the same time other operations, particularly the ones necessary to avoid a stoppage situation. For example, if the crane is hoisting a very heavy weight, the extensions of an arm could be extended to a determined length, which cannot be further increased because this would entail risks of breaking or flipping over the crane. In such circumstances, the extensions are prevented from being further lengthened, however it is possible to retract the extensions for preventing an overloading situation.
When there is a stoppage, the operator often has problems in understanding which operations are executable or not. Therefore, visual systems adapted to help the operator execute the correct operations for preventing stoppage conditions, have been proposed.
Particularly, there are radio commands provided with luminous icons, in turn associated to specific movements of a crane, which, by acting on one of the levers, which commands a particular movement, indicate, by a “stop” signal, that the required movement is not available. A similar radio command is described in the international application WO 2006/036115. According to such solution, however the operator must follow a trial-and-error procedure and verify, from time to time, according to his/her experience, if the movement, necessary for overcoming the stoppage situation, is correct or not. Moreover, according to this solution, the operator does not receive any indication regarding the allowable direction and is aware of it, also in this case, only after trials.
Further known devices are provided with a display which shows, always after a specific request of the operator, a schematic image of the overall crane and of all the movable parts thereof, with an indication of all the available and unavailable movements. Such system, even though is complete from a point of view of the information available to the operator, however is difficult to be examined, particularly in case of a crane having several degrees of freedom. Actually, the operator receives by a single display the situation of all the enabled and disabled movements of the crane, and autonomously must understand it and also associate each part of the crane, shown in the display, to a specific command of the radio command. Such operation can require a lot of time. Moreover, the risk of errors for the operator is still high.